Fix continual setting of task state to queued.
Don't call stop on the GUI updater until it exists.

Fixes gcylc traceback on starting up with no suite selected and then
quitting immediately.
Merge pull request #608 from hjoliver/gcylc.fix-quit-bug

Don't call stop on the GUI updater until it exists.
Undo lisifying of argument to is_currently
Merge pull request #606 from arjclark/fix-repeated-log-queued

Fix continual setting of task state to queued.